Curtainwall architecture, such as in office building and the like, includes both vision areas where windows are provided and opaque areas that are typically referred to as spandrels. Coated articles for spandrels are typically used in a manner similar to windows in that they enclose building structures, and are often provided at the exterior of a building or structure. Spandrel areas are formed by panels that are either opaque or substantially opaque, with the opaqueness or substantially opaqueness often being provided by an enamel coating or the like applied to a substrate.
Spandrel coatings are generally employed to conceal or mask portions of a structure or building that are not aesthetically pleasing if visible from the exterior of the structure or building. For example, coated articles for spandrels may be used to conceal from view one or more of the following from view from the exterior of a building: floor slabs, air conditioning equipment, heating ducts and so forth. Coated articles for spandrels may instead or also be used to maintain privacy or security such as at the ground level of a building.
Since the exterior of an office building or apartment building includes a combination of windows and coated articles for spandrels, the color and/or optical appearance of spandrel coatings is not irrelevant. In certain situations, it is desirable to have the coated articles for spandrels substantially match or otherwise compliment the appearance of windows (e.g., insulating glass or IG window units) of the building when viewed from the building exterior.
FIG. 1 is a cross sectional view of a conventional coated article for use in spandrel applications. The spandrel coated article of FIG. 1 includes a coating on glass substrate 1 that includes titanium oxide layer 3, metallic titanium layer 5, silicon nitride layer 7, and colored ceramic enamel frit layer 9 as an overcoat layer of the overall coating. Unfortunately, the spandrel coating of FIG. 1 is difficult to control and/or predict with respect to its optical characteristics. For instance, the FIG. 1 coating tends to have inconsistent glass side reflectance and/or color characteristics when used on surface #2 of monolithic spandrel applications (i.e., when used on the interior surface of a spandrel panel adjacent the building interior, as opposed to on the exterior surface of the panel).
Moreover, heat treatment is problematic for the spandrel coated article of FIG. 1 because the glass side reflectance and/or color characteristics of the coated article are not thermally stable. In other words, heat treatment such as thermal tempering tends to cause unpredictable dramatic changes in the optical characteristics (e.g., glass side reflectance and/or glass side reflective color) of the coated article of FIG. 1.
In particular, coated articles of FIG. 1 experience ΔE*g (glass side reflective) due to heat treatment of well over 10.0 which is very large. This large ΔE*g value indicates that the conventional coated article is not thermally stable, in that its glass side reflective optical characteristics change very much upon heat treatment such as thermal tempering. This is undesirable in that the final optical characteristics of the coated article then become too dependent upon processing conditions such as furnace conditions, heat treatment time/temperature and/or the like. It is noted that a detailed discussion of the ΔE* calculation and meaning may be found in U.S. Pat. Nos. 6,908,679, 6,558,800 and/or 6,524,714, the disclosures of all of which are hereby incorporated herein by reference.
Thus, it will be appreciated that there exists a need in the art for a spandrel (or spandrel panel) that is more predictable and/or consistent with respect to its optical characteristics (e.g., color, reflection, and/or the like), especially after heat treatment such as thermal tempering or the like. It would be desirable if a coated article could be provided having a lower ΔE*g value due to heat treatment, which is indicative of a more thermally stable product.